This invention relates in general to continuous seam welders and, more specifically, to a system for accurate tracking of a seam during sink welding.
A number of different systems have been developed for guiding a welding torch along a desired path relative to a workpiece during welding. The most simple arrangements merely move the welder or workpiece along a preselected path. These arrangements tend to be relatively inaccurate, since the moving mechanism will generally not exactly follow the ideal path. Moving very large workpieces past a welding station without deviating from the intended path is very difficult. Also, these systems do not provide for irregularities in workpiece size or shape.
Because of these problems, a number of seam tracking systems have been developed. Many use a mechanical servo arrangement in which a sensor or feeler rides along the seam ahead of the welding head. However, these do not provide precisely accurate tracking because of mechanical backlash and the need to have the sensor sufficiently far ahead of the welder to avoid interference with the welding operation. The greater the separation between sensor and welder, the greater the chance for error resulting from seam irregularities between the two locations. Also, mechanical systems are only usable with joints having gaps large enough to receive the sensing means.
In an attempt to provide tracking of seams in structures of widely varying shapes, U.S. Pat. No. 3,575,364 provides a flexible track secured to the structure adjacent to the seam. while this system has a variety of applications, its accuracy is limited by the accuracy of track placement.
Attempts have been made to use electronic sensing and control of seam welders. For example, the system disclosed in U.S. Pat. No. 3,532,807 uses a television camera guided servo system. However, this system used television scanning parallel to the weld seam, resulting in an unstable video signal making detection unreliable, especially with curved structures or seams. Also, the use of a closed loop servo system requires both torch and camera be mounted on a single carriage, with attendant problems of magnetic interference to the camera, vibration transmission to the camera and carriage size.
Thus, there is a continuing need for an improved seam tracking system for welders.